net.sf.mmm.client.ui.gwt.widgets.handler.AbstractMouseDragHandler.java Source code

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Here is the source code for net.sf.mmm.client.ui.gwt.widgets.handler.AbstractMouseDragHandler.java

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/* Copyright (c) The m-m-m Team, Licensed under the Apache License, Version 2.0
 * http://www.apache.org/licenses/LICENSE-2.0 */
package net.sf.mmm.client.ui.gwt.widgets.handler;

import com.google.gwt.dom.client.NativeEvent;
import com.google.gwt.event.dom.client.MouseDownEvent;
import com.google.gwt.event.dom.client.MouseDownHandler;
import com.google.gwt.event.dom.client.MouseMoveEvent;
import com.google.gwt.event.dom.client.MouseMoveHandler;
import com.google.gwt.event.dom.client.MouseUpEvent;
import com.google.gwt.event.dom.client.MouseUpHandler;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.user.client.Event;
import com.google.gwt.user.client.Event.NativePreviewEvent;
import com.google.gwt.user.client.ui.Widget;

/**
 * This is the abstract base class for a handler that allows moving or resizing with the mouse.
 * 
 * @author Joerg Hohwiller (hohwille at users.sourceforge.net)
 * @since 1.0.0
 */
public abstract class AbstractMouseDragHandler implements MouseDownHandler, MouseUpHandler, MouseMoveHandler,
        Event.NativePreviewHandler, AbstractCustomHandler {

    /** The initial x position while dragging the mouse. */
    private int mouseX;

    /** The initial y position while dragging the mouse. */
    private int mouseY;

    /**
     * The {@link HandlerRegistration} for the global mouse-listener registration while dragging or
     * <code>null</code>.
     */
    private HandlerRegistration registration;

    /**
     * The constructor.
     */
    public AbstractMouseDragHandler() {

        super();
    }

    /**
     * @return the mouseX
     */
    public int getMouseX() {

        return this.mouseX;
    }

    /**
     * @return the mouseY
     */
    public int getMouseY() {

        return this.mouseY;
    }

    /**
     * This method can be overridden for dynamic activation of this handler.
     * 
     * @return <code>true</code> if this handler is active, <code>false</code> if it is inactive (ignores all
     *         events and does nothing).
     */
    protected boolean isActive() {

        return true;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public final void onMouseDown(MouseDownEvent event) {

        if (!isActive()) {
            return;
        }
        this.mouseX = event.getClientX();
        this.mouseY = event.getClientY();

        initializeOnMouseDown(event);

        // assert (this.registration == null);
        this.registration = Event.addNativePreviewHandler(this);
        // prevent other things such as text selection while dragging...
        event.preventDefault();
    }

    /**
     * Override to add initialization logic to {@link #onMouseDown(MouseDownEvent)}.
     * 
     * @param event is the initial {@link MouseDownEvent}.
     */
    protected void initializeOnMouseDown(MouseDownEvent event) {

        // Nothing by default...
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void onPreviewNativeEvent(NativePreviewEvent event) {

        int eventType = event.getTypeInt();
        if (eventType == Event.ONMOUSEMOVE) {
            NativeEvent nativeEvent = event.getNativeEvent();
            int button = nativeEvent.getButton();
            if (button == NativeEvent.BUTTON_LEFT) {
                onMouseMove(nativeEvent.getClientX() - this.mouseX, nativeEvent.getClientY() - this.mouseY,
                        nativeEvent);
            } else {
                onMouseUp(null);
            }
        } else if (eventType == Event.ONMOUSEUP) {
            onMouseUp(null);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void onMouseMove(MouseMoveEvent event) {

        onMouseMove(event.getClientX() - this.mouseX, event.getClientY() - this.mouseY, event.getNativeEvent());
    }

    /**
     * @see #onMouseMove(MouseMoveEvent)
     * 
     * @param deltaX is the relative movement of the mouse position on X-axis.
     * @param deltaY is the relative movement of the mouse position on Y-axis.
     * @param nativeEvent is the {@link NativeEvent} that triggered this invocation.
     */
    protected abstract void onMouseMove(int deltaX, int deltaY, NativeEvent nativeEvent);

    /**
     * {@inheritDoc}
     */
    @Override
    public void onMouseUp(MouseUpEvent event) {

        // DOM.releaseCapture(((Widget) event.getSource()).getElement());
        if (this.registration != null) {
            this.registration.removeHandler();
        }
        this.registration = null;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void register(Widget widget, HandlerRegistrationCollector collector) {

        widget.sinkEvents(Event.ONMOUSEDOWN);
        HandlerRegistration handlerRegistration = widget.addDomHandler(this, MouseDownEvent.getType());
        if (collector != null) {
            collector.addHandlerRegistration(handlerRegistration);
        }
    }
}